The invention relates to golf balls and, more particularly, to golf balls having one or more core layer(s), cover layer(s) and/or intermediate layer(s), wherein at least one of the layers is formed of a poly(trimethylene terephthalate) (xe2x80x9cPTTxe2x80x9d) composition and wherein the PTT composition is either 100 weight percent PTT or a PTT blend with other polymers. The invention also relates to methods for making such golf balls from PTT compositions. Golf balls produced in accordance with the present invention are characterized by improved properties including abrasion resistance, cut resistance and durability.
Three-piece, wound golf balls with balata covers are preferred by most expert golfers. These balls provide a combination of distance, high spin rate, and control that is not available with other types of golf balls. However, balata is easily damaged in normal play, and, thus, lacks the durability required by the average golfer.
In contrast, amateur golfers typically prefer a solid, two-piece ball with an ionomer cover, which provides a combination of distance and durability. Because of the hardness of the ionomer cover, these balls are almost impossible to cut, but they also have a very hard xe2x80x9cfeelxe2x80x9d, which many golfers find unacceptable, and a lower spin rate, making these balls more difficult to draw or fade. The differences in the spin rate can be attributed to the differences in the composition and construction of both the cover and the core.
Many attempts have been made to produce a golf ball with the control and feel of a wound balata ball and the durability of a solid, two-piece ball, but none have succeeded totally. For example, U.S. Pat. No. 4,274,637 to Molitor discloses two- and three-piece golf balls having covers completely or partially formed from a cellular polymeric material to improve backspin, but does not provide any examples that compare the spin rates of the disclosed golf balls with those of prior art balls.
U.S. Pat. No. 5,002,281 to Nakahara et al. discloses a three-piece solid golf ball having an ionomer cover and a solid core consisting of a soft inner core surrounded by a hard outer shell, where the difference in the hardness of the two parts of the core is at least 10 on the JIS-C scale.
Similarly, U.S. Pat. No. 4,781,383 to Kamada et al. discloses a solid, three-piece golf ball, having an ionomer cover and a core with inner and outer layers, where the inner layer has a diameter of 24 to 29 mm and a Shore D hardness of 15 to 30, and the outer layer has a diameter of 36 to 41 and a Shore D hardness of 55 to 65.
European Patent Application 0 633 043 discloses a solid, three-piece golf ball with an ionomer or balata cover, a center core, and an intermediate layer. The center core has a diameter of at least 29 mm and a specific gravity of less than 1.4. The intermediate layer has a thickness of at least 1 mm, a specific gravity of less than 1.2, and a hardness of at least 85 on the JIS-C scale.
Blending a polymer and an ionomer is one approach which has been used in forming golf ball covers, and thus golf balls, with improved properties. One such combination is disclosed in U.S. Pat. No. 4,858,924 to Saito, which teaches the use of a thermoplastic resin with a flexural modulus of 1,500 to 5,000 kg/cm2 blended with an ionomer to form the cover of a golf ball. Particularly, polyamide elastomer, urethane elastomer, styrene-butadiene copolymer elastomer and polyester elastomer are said to be preferred when used alone or blended with a matrix resin, that is, another like flexible thermoplastic resin. The polyester elastomers are said to include block copoly(ether-esters), block copoly(lactone-esters) and aliphatic and aromatic dicarboxylic acid copolymerized polyesters. However, the Saito patent does not teach the use of the polyester, poly(trimethylene terephthalate), in a golf ball cover.
In pigmented golf ball covers, the color of the cover is enhanced by the use of optical brightener in combination with a pigment system. The use of an optical brightener is desired especially when the cover material is not white in appearance. By incorporating an optical brightener in the cover, the need for a supplemental paint coating can be reduced or eliminated. U.S. Pat. No. 4,679,795 to Melvin et al. discloses blends of optical brighteners with the following golf ball materials: polyolefins and their copolymers; polyurethanes; polyamides, polyamide blends with SURLYN(copyright), polyethylene, ethylene copolymers and EPDM; vinyl and acrylic resins; thermoplastic rubbers such as urethanes, styrene block copolymers, copoly(ether-amides) and olefinic thermoplastic rubbers; and thermoplastic polyesters such as poly(ethylene terephthalate) (hereinafter xe2x80x9cPETxe2x80x9d), poly (butylene terephthalate) (hereinafter xe2x80x9cPBTxe2x80x9d) and PETG. The reference contains no teaching, however, to use poly(trimethylene terephthalate) (hereinafter xe2x80x9cPTTxe2x80x9d) in a pigmented golf ball cover with an optical brightener. In fact, none of the above disclosures describe the use of poly(trimethylene terephthalate) in golf balls.
Poly(trimethylene terephthalate) has been used mainly in carpet fiber and textile applications. However, similarities in tensile strength, flexural modulus, specific gravity, mold shrinkage, melting point, and glass transition temperature suggest that poly(trimethylene terephthalate) can be a good substitute for polyamides and polyamide blends used in golf ball covers, intermediate layers, and cores.
U.S. Pat. No. 5,981,654 is directed to compositions and methods for forming golf ball covers, cores and intermediate layers, wherein the composition comprises a blend of a polyamide and poly(trimethylene terephthalate) without optical brightener. The disclosure of that reference, however, contains no teaching or suggestion to formulate a composition without polyamide and with optical brightener.
As a result, a need exists for a golf ball incorporating poly(trimethylene terephthalate) and blends of poly(trimethylene terephthalate), having the feel and spin of balata covered balls and the durability and distance of ionomer covered balls. The present invention provides such a golf ball.
The present invention is directed to golf balls and in particular, to golf balls having at least one layer comprising poly(trimethylene terephthalate), either alone or in blends with other polymers wherein, when such other polymers are present, i.e., in the blend, they do not include a polyamide polymer.
While poly(trimethylene terephthalate) will generally be used in forming some or all of the cover layer(s) of the golf ball, it may also or alternatively comprise some or all of the core layer(s), and/or intermediate layer(s). The invention includes one-piece golf balls comprising poly(trimethylene terephthalate), either alone or as a blend, with other polymers, as well as two-piece and three-piece golf balls comprising at least one cover layer and a core.
In accordance with the invention, in a first embodiment, the golf ball has at least one layer, i.e., a core layer, an intermediate layer and/or a cover layer, comprised of a poly(trimethylene terephthalate) composition, wherein the poly(trimethylene terephthalate) composition is substantially free of polyamide polymer. As used herein, the term xe2x80x9cpoly(trimethylene terephthalate) compositionxe2x80x9d refers to both 100 wt % poly(trimethylene terephthalate) as well as a poly(trimethylene terephthalate) blend comprising from about 1 to about 99 wt % poly(trimethylene terephthalate) and from about 99 to about 1 weight percent of a non-polyamide second polymer component. Optionally, the second polymer component may be a polyurethane, an epoxy resin, a polystyrene, an acrylic, a polyethylene, a polyester, a polycarbonate or an acid copolymer or its ionomer derivative or blends thereof.
In another embodiment, the PTT-containing layer has a foamed structure. For a layer formed of a poly(trimethylene terephthalate) composition having a foamed structure, the preferred flexural modulus ranges from 1000 to 150,000 psi. For golf ball covers having a layer formed of a poly(trimethylene terephthalate) composition with a foamed structure, the layer preferably has a Shore D hardness of from about 15 to about 80 and a thickness of from about 0.005 to 0.125 inch. Generally, for golf balls having a layer formed of a poly(trimethylene terephthalate) composition with a foamed structure, the layer has a Shore D hardness of from about 15 to about 80 and a thickness of from about 0.005 to 0.125 inch. The core preferably has a diameter of from about 1 to 1.63 inch.
Where the layer comprising a poly(trimethylene terephthalate) composition is situated in an outer portion of the core, the core comprises a liquid center or a solid polymeric center. Optionally, the core further comprises an elastomer. Preferably the poly(trimethylene terephthalate) composition comprises an elastomer, such as polybutadiene, a metallic derivative of diacrylate, and from about 1 to about 75 parts by weight poly(trimethylene terephthalate). Preferably, the PTT is present in an amount of about 1 to about 50 parts by weight. More preferably, the PTT is present in an amount of about 5 to about 40 parts by weight. Most preferably, the PTT is present in an amount of about 5 to about 25 parts by weight.
In another embodiment, the invention is directed to a golf ball comprising a cover and a core, wherein the cover comprises a poly(trimethylene terephthalate) composition.
In a still further embodiment, the invention is directed to three-piece golf balls comprising at least one cover layer, at least one core layer and at least one intermediate layer between the cover and the core, where at least one layer comprises a poly(trimethylene terephthalate) composition. Optionally, the poly(trimethylene terephthalate) is blended with a non-polyamide second polymer component and the second polymer component may be a polyurethane, an epoxy resin, a polystyrene, an acrylic, a polyethylene, a polyester, a polycarbonate or an acid copolymer or its ionomer derivative or blends thereof; and the poly(trimethylene terephthalate) composition may be foamed or unfoamed. Preferably, the blend comprises about 10 to about 75 weight percent of poly(trimethylene terephthalate) and about 90 to about 25 weight percent of the second polymer component. More preferably, the blend comprises about 15 to about 40 weight percent of poly(trimethylene terephthalate) and about 85 to about 60 weight percent of the second polymer component.
Further, the core of the three-piece golf ball comprise a liquid or solid center. Optionally, the liquid or solid center may be wrapped in elastomeric windings, which may be comprised of a poly(trimethylene terephthalate) composition. As used herein, the liquid center comprises an outer envelope containing a liquid, wherein the envelope is formed of a poly(trimethylene terephthalate) composition.
In another embodiment, the invention provides a method of making a two-piece golf ball. The method comprises the steps of forming a golf ball core by conventional means and subsequently forming a cover around the core by either compression molding preformed half-shells of cover stock material comprising poly(trimethylene terephthalate) about the core or by injection molding cover stock material comprising a poly(trimethylene terephthalate) composition, wherein the poly(trimethylene terephthalate) composition may be foamed or unfoamed. Optionally, the poly(trimethylene terephthalate) may be blended with a polyurethane, epoxy resin, polyethylene, polyester, polystyrene, polycarbonate, acrylic or acid copolymer or its ionomer derivative or blends thereof. Golf balls that are manufactured in this manner will have mechanical properties superior to otherwise similar golf balls without poly(trimethylene terephthalate).
In an additional embodiment, this invention provides a method of making a multi-layer golf ball, which comprises forming a core layer, forming at least one intermediate layer about the core layer, and forming a cover layer over the at least one intermediate layer, wherein at least one of the layers comprises a poly(trimethylene terephthalate) composition and may be foamed or unfoamed. Optionally, the poly(trimethylene terephthalate) of the core layer, intermediate layer and/or cover layer may be blended with one or more conventional ionomeric and/or non-ionomeric thermoplastic polymers. Preferably, the non-ionomer thermoplastic elastomer polymer is selected from the group consisting of a block copolymer of copoly(esterxe2x80x94ester), a block copolymer of copoly(ester-ether), a block copolymer of copoly(urethane-ester), a block copolymer of copoly(urethane-ether), a block polystyrene thermoplastic elastomer comprising an unsaturated rubber, a block polystyrene thermoplastic elastomer comprising a functionalized substantially saturated rubber, a thermoplastic and elastomer blend comprising polypropylene and ethylene-propylene-diene monomer terpolymer or ethylene-propylene copolymer rubber, where the rubber is dynamically vulcanized, poly(ethylene terephthalate), poly(butylene terephthalate), poly(vinyl alcohol), poly(vinyl acetate), poly(silane), poly(vinylidene fluoride), acrylonitrile-butadiene-styrene copolymer, olefinic polymers, their copolymers, including functional comonomers, and mixtures thereof.
The use of a foamed poly(trimethylene terephthalate) composition also allows the golf ball designer to adjust the density or mass distribution of the ball to adjust the angular moment of inertia, and, thus, the spin rate and performance of the ball. Foamed materials also offer a potential cost savings due to the reduced use of polymeric material. Where at least a portion of the core is formed from a foamed poly(trimethylene terephthalate) composition, a density increasing filler material can be added to the cover or the intermediate layer to distribute the mass of the ball towards the outer surface and increase the angular moment of inertia. Similarly, where the layer forms at least a portion of the cover, the density increasing filler material can be added to the core to decrease the angular moment of inertia. Alternatively, where the layer forms at least a portion of the intermediate layer, a density increasing filler material can be added to either the cover or the core.
The novel golf ball of the invention offers improved mechanical properties in comparison to golf balls disclosed in the prior art, for instance, improved abrasion resistance, cut-resistance and durability. Further these balls also provide enhanced distance (i.e., resilience) without adversely affecting, and in many instances while improving, their xe2x80x9cplayabilityxe2x80x9d characteristics, i.e., their impact resistance, spin, xe2x80x9cclickxe2x80x9d and xe2x80x9cfeelxe2x80x9d, compression, etc.